European Patent Publication EP 1 593 444 A1 discloses a punching apparatus that has a punching tool that is movable along a longitudinal axis. The punching apparatus has a drive device to move the punching tool in a linear, reciprocating movement that comprises a downward stroke and a return stroke. During the downward stroke of the punching apparatus engaged in punching the metal plate, the metal plate exerts a reaction force on the punching tool in a direction opposite of the direction of movement of the punching tool. The punching tool has a first component that is moved by the drive device with a predetermined first law of motion during the downward stroke and the return stroke. The punching tool also has a second component, which, during operation, cooperates with a ram to punch the metal plate. The second component is connected to the first component in a sliding manner and is positioned between the first component and the workpiece. Provided that the reaction force is below a predetermined value, the second component is moved axially substantially with the same law of motion as the first component during the downward stroke. The punching apparatus also has pressure-exerting means in order to move the second component with a second law of motion, different from the first, when the reaction force corresponds at least to the predetermined value.
The first component and the second component of the punching tool are moved concurrently by a drive device that comprise an electric motor acting on a threaded spindle. If the predetermined value of the reaction force is exceeded, the force of the electric motor is insufficient to punch through the workpiece. In this case, the pressure-exerting means are activated in order to enhance the force exerted on the workpiece and to punch through the workpiece. The first component is in this case moved toward the second component, which bears against the workpiece and is thus initially prevented from continuing to move downward. As a result of the relative movement between the first component and the second component, the hydraulic force on the second component is enhanced. If the first component is moved back upward after the workpiece has been punched through, the first component initially moves away from the second component along the stroke axis until the first component bears against a stop of the second component, such that it can entrain the second component upward during the return stroke.
European Patent Publication EP 0 575 343 B1 discloses an apparatus for carrying out a two-stage linear movement, in which a movable unit has a hydraulic piston with a cavity into which a plunger piston projects. The hydraulic piston bears a spindle that is rotatable by an electric motor, and the plunger piston is axially displaceable by means of the spindle in the hydraulic piston and a hydraulic cylinder, in order to build up pressure in the latter. The apparatus can have an auxiliary cylinder that is connected to the cylinder chamber of the hydraulic cylinder. Located in the auxiliary cylinder is a piston that is coupled to the hydraulic piston via a carrier plate and moves uniformly with said hydraulic piston.
US Patent Publication US 2009/0084277 discloses an apparatus that has a connecting mechanism for connecting an output shaft to an input shaft such that they are not movable relative to one another. To apply high pressure to the output shaft, a fluid pressure mechanism is provided, which is configured to establish a hydraulic connection between the output shaft and the input shaft in order to move them relative to one another. The connecting mechanism detects the contact of the output shaft with the workpiece and releases the connection between the output shaft and the input shaft. If, after the workpiece has been punched through, the input shaft is returned to a position prior to application of high pressure, the connection can be re-established automatically by the connecting mechanism. A similar apparatus, in which a through-bore extends in an axial direction from a second fluid chamber, which is formed between the output shaft and a fastening part, is disclosed in European Patent Publication EP 1 652 660 A1.
Japanese Patent Publication JP 2000-141092 discloses a punching machine that, in the case of a constant-power motor, is intended to allow both a movement with a low pressure force and a high speed prior to the punching operation and a movement with a high pressure force and a low speed during the punching of a workpiece. For this purpose, an oil chamber is formed in a housing and a first piston is provided, which is fastened at its front end to the rear end of a second piston. The first piston has a pressurizing surface and the second piston has at its rear end a pressure receiving surface, the area of which is greater than the area of the pressurizing surface.
PCT Patent Publication WO 2011/079333 A2 discloses a drive apparatus for a bending press, which comprises a stationary press beam and a press beam that is adjustable by means of a beam adjusting device having a hydraulic linear actuator. The linear actuator has a first piston arrangement having a first piston that subdivides a cylinder chamber into a first pressure chamber and a second pressure chamber. The linear actuator also has, in a further cylinder chamber, a further piston arrangement having a further piston and at least one further pressure chamber. The first piston arrangement and the second piston arrangement are coupled together.